The photovoltaic power generation technology, as a renewable energy source power generation technology, has been widely used all over the world. The direct current outputted from a photovoltaic array is converted into the alternating current by an inverter, and thus the alternating current, as the clean energy source, is transmitted to a power grid. With the development of the photovoltaic industry, the probability that an accident occurs during the operation is increasing.
Since the photovoltaic array formed by multiple photovoltaic modules connected in series with each other has a high voltage, a rapid shutdown (RS) mechanism is put forward for a photovoltaic system in the National Electrical Code (NEC) 2017, 690.12, to improve the safety of the photovoltaic system. It is required that, a voltage between conductors within a range of one foot and a voltage between a conductor and the ground cannot exceed 80V after the shutdown protection is performed on the photovoltaic array.
The existing major methods are described as follows.
A module shutdown technology is generally used. In which, each of modules is connected to a rapid shutdown device, and the module is connected in series with a switch included in the shutdown device. In the normal operation, the switch is turned on, and the module may output electric energy. When a shutdown instruction is received, the rapid shutdown device controls the switch to be turned off, so that the modules are open-circuited relative to each other, and the output voltage is zero.
For the protection method in which a module is connected to a rapid shutdown device, each photovoltaic module is required to be connected to one rapid shutdown device, which results in a high cost. In addition, in the normal power generation process, switches of multiple rapid shutdown devices corresponding to a photovoltaic string may be connected in series with each other, which results in a large conduction loss and low power generation efficiency.